Understanding N 2 O Emissions in African Ecosystems: Assessments from a Semi-Arid Savanna Grassland in Senegal and Sub-Tropical Agricultural Fields in Kenya
Résumé
This study is based on the analysis of field-measured nitrous oxide (N 2 O) emissions from a Sahelian semi-arid grassland site in Senegal (Dahra), tropical humid agricultural plots in Kenya (Mbita region) and simulations using a 1D model designed for semi arid ecosystems in Dahra. This study aims at improving present knowledge and inventories of N 2 O emissions from the African continent. N 2 O emissions were larger at the agricultural sites in the Mbita region (range: 0.0 ± 0.0 to 42.1 ± 10.7 ngN m −2 s −1) than at the Dahra site (range: 0.3 ± 0 to 7.4 ± 6.5 ngN m −2 s −1). Soil water and nitrate (NO 3 −) contents appeared to be the most important drivers of N 2 O emissions in Dahra at the seasonal scale in both regions. The seasonal pattern of modelled N 2 O emissions is well represented, though the model performed better during the rainy season than between the rainy and dry seasons. This study highlighted that the water-filled pore space threshold recognised as a trigger for N 2 O emissions should be reconsidered for semi-arid ecosystems. Based on both measurements and simulated results, an annual N 2 O budget was estimated for African savanna/grassland and agricultural land ranging between 0.17-0.26 and 1.15-1.20 TgN per year, respectively.
Domaines
Ecosystèmes
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